petroleum geology petroleum systems eor 101

Petroleum GeologyPetroleum Systems

EOR 101

Petroleum systemWhat is a reservoir ?

Formation of hydrocarbons

About the reservoirsResources

Enhanced Oil Recovery (EOR)Why considering EOR ?

Chemistry Principles of Polymer Injection

Polymer solvent interactionPolymer degradation and strategies to minimize it

Use of surfactants and alkali in EOR

SNF in Enhanced Oil RecoveryMulti-purpose Engineering Services

Projects

0405

06

08

10121416

1820

Summary

4

A petroleum reservoir, or oil and gas reservoir, is a subsurface pool of hydrocarbons contained in po-rous or fractured rock formations. The naturally occurring hydrocarbons, such as crude oil or na-tural gas, are trapped by overlaying rock forma-tions with lower permeability. The vast majority of hydrocarbons are trapped within sedimentary rocks, formed at the earth surface though several process including weathering, precipitation and biogenic activity. We can distinguish:

What is a reservoir ?

Lithology

Sandstone

Carbonate

Other (shale...)

60%

30%

10%

21%

37%

42%

37%

61,5%

2,5%

Oil bearing reservoirs

Abundance of rock type

Production by rock type

Drilling rig

Cores are drilled to study the reservoir

Petroleum system

Clastic rocks formed from pre-existing rocks by erosion, transport, transformation and deposition. These include sandstones, conglomerates, sils-tones and shales.

Carbonates rocks formed from organic constituents and chemical precipitates; including limestones, dolomites and chalks.

25 c

m

5 cm 100 µm

5

Petroleum system

The petroleum system consists of a mature source rock, migration pathway, reservoir rock, trap and seal. Appropriate relative timing of formation of these elements and the processes of generation, migration and accumulation are necessary for hydrocarbons to accumulate and be preserved.Hydrocarbons are generated from the thermo-cracking of organic matter accumulated in a source rock. It requires temperature (>50°C) and time.

Formation of hydrocarbons

Many types of hydrocarbon traps exist:

Anticline, Fault, Stratigraphic trap, Salt dome, ...

Porous rockNon-porous rockSaltGasOil

Anticline

Stratigraphic trap Salt dome

Fault

+

++

+

Biomarkers

Oil

Biogenic methane

Wet gas

Dry gas

Graphite

Quantity of hydrocarbons generated

DiagenesisM

etagenesisCatagenesis

Imm

ature zoneGas w

indowoil w

indow

Surface

Depth

6

Characteristics of oil and gas generated depend on the type of organic matter and the maturation process. People also make a distinction between conventional and unconventional resources: unconventional plays require specific and often expensive techniques to be produced.

Unconventional resources: example of tight gas reservoirsIn tight gas reservoirs, the pores are irregularly distributed and poorly connected by very narrow capillaries resulting in very low permeability. Gas flows through these rocks at generally low rates and special methods are necessary to produce this gas such as hydraulic fracturing.

Unconventional play By opposition with conventional systems, un-conventional resources are not easily producible with existing technologies (low permeability re-servoirs or viscous oil)

Source-rock hydrocarbonsShale Oil or Shale Gas directly extracted from the source rock by fracturation.

Data source : US Energy Information Administration from Oil and Gas Journal (2007) Oil includes crude oil and condensate

Asia & Oceana

North America

Central & South America

Europe

Eurasia

Africa

Middle East

3%

9%

56%

16%

8%

1%

7%

Resources

About the reservoirs

Acronyms

OOIP : Original Oil in PlaceIOR : Improved Oil RecoveryEOR : Enhanced Oil RecoveryChem EOR : Chemical EORPF : Polymer FloodingSP : Surfactant and Polymer FloodingASP : Alkaline Surfactant Polymer FloodingPAM : PolyacrylamideHPAM : Partially Hydrolized PolyacrylamideMW : Molecular WeightDa : Dalton (MW unit of measure)IFT : Interfacial tensionPSU™ : Polymer Slicing UnitPIU™ : Polymer Injection Unit

7

Conventional ReservoirsSmall Volumes, Easy to Develop

Unconventional Reservoirs Large Volumes, Hard to Develop

Huge Volumes, Difficult to Develop

Oil

Tight OilHeavy Oil

Bituminous Sands

Oil Shale

Gas

Acce

sibi

lity

Cost

Coal Bed MethaneGas Shales

Tight Gas Sands

Gas Hydrates

Tight gas sandstone : (voids in blue).

Resource pyramid

8

Why consider EOR ?

Enhanced Oil Recovery ( EOR)

The production of hydrocarbons is usually divided into 3 stages :

Primary depletionOil is naturally produced thanks to the energy initially stored within the reservoir;,Secondary productionIn order to maintain the production and the pressure in the reservoir, water (or sometimes gas) is injected to push the hydrocarbons;

Tertiary productionInjection of specific substances to increase recovery (gas, chemicals, steam...).

to exploration & extraction increase (ultra-deep offshore, artic circle...). As such, increasing the recovery factor by 1% would translate into 60 billion extra barrels.EOR applies to known reservoirs, infrastructure is already in place and the market for hydrocarbons is available. Polymer flooding is a proven, cost-effective EOR

technique with over 40 years of commercial application that allows recovering from 5 to 15% of additional oil. The best commercial projects have produced about 1 incremental barrel of oil for each $1 to $3 of polymer (onshore).The addition of water-soluble polyacrylamides increases water viscosity and helps push bypassed oil more efficiently. A first step consists in evaluating the potential through a pilot injection.A pilot is a good way to prove the efficiency: Fast deployment (skid-mounted systems) Low costs Low risks

Primary productionNatural flow and artificial lift techniques (pumps)

Secondary recoveryWater flooding or pressure maintenance

Tertiary recoveryEnhanced Oil Recovery me-thods

GasCO2, Nitrogen, Air

ThermalSteam In Situ combustion,

Hot water

ChemicalPolymers (PF)

Surfactant Polymer (SP)Alkaline reagents (ASP)

OtherMicrobial

Time

Oil

Prod

uctio

n ra

te

Poly

mer

in

ject

ion

Incremental

EOR

35% of Oil Originally In Place (OOIP) is produced after primary and secondary productions. It means that 65% of oil remains after secondary recovery, trapped into pores by different forces.

There is little doubt that the worldwide demand for oil will increase in the long term. But reserves are not generally replaced and it would require the discovery of new «giant» fields.

Drilling alone is expensive: it requires a large capital investment, and drilling rate is inversely correlated with discovery rate. The costs linked

Production well

Injection fluid Injection pump

Injection well

9

Enhanced Oil Recovery (EOR)

Modular injection systems can be tied-in to existing injection lines: no need to build new infrastructure, use of available water for polymer injection.After this stage, full-field deployment can be considered. Polymer flooding reduces costs related to water handling. The process requires less water to recover the same amount of oil, so the costs linked to water treatment & handling are

reduced. Produced water containing polymer can be reused for further injection. In the long-term, polymer flooding can be less expensive than waterflooding. Preferable conditions for polymer injection are light to medium-heavy oil, low salinity, medium to high reservoir permeability, low temperature (below 100°C). Even though, new polymers can resist harsh conditions: 140°C and around 200g/L total salinity.

The earlier, the better: implementing polymer flooding early in the life of a field helps increase the final amount of oil recovered.

1976 - 1982History of chemical EOR projects

1989 - 2000

2010 - 2015

More than 320 chemical injections in the USEast CoalingaTaber – ManvilleWest Yellow Creek

North Burbank

Large success in ChinaDaqing : world’s largest polymer injection, resulting in a 12% increase in recovery of the OOIP.

More than 50 polymer injections. More than 170 projects.China (Daqing cont’d)Oman PDO MarmulSurinameIndonesiaCanada (more than 30 polymer inj.)Russia & KazakhstanEuropeLatin AmericaIndia

Modular systems tied-in to existing injection lines

Oil viscosity (cp)

+

80

60

40

20

0.11 10 100 103

Worldwide Average RF ~35%

40 to 50 %Water or gas

injection

40 to 50 %Water

injection

20 to 30 %Water

injection5 to 20 % Water injection

Primary and Secondary oil recovery factor% Recovery factor

RF ~60%

+10 to 20 %Alkaline / Surfactant / Polymer

+5 to 15 %Polymer only

+5 to 15 %Polymer only

Oil viscosity (cp)

+

80

60

40

20

0.11 10 100 103

Tiertiary oil recovery factor

30 to 40 %Water or gas

injection

30 to 40 %Water

injection

20 to 30 %Water

injection5 to 15 % Water injection

% Recovery factor

10

Can be run in parallel and shortened (order of weeks) if using standard skids

Some key figures:Polymer is injected over 5 to 25 years.

Typical injection concentrations range from 1000 to 1500 ppm active.

Injection of at least 0.3 pore volume: the more the better.

Injection of high viscosity slug recommended in some cases.

Incremental oil with polymer ranges from 5% to 15% OOIP.

Polymer injection = viscous waterflood limited risk

Polymer injection applies when the mobility ratio during a waterflood is unfavorable or when the reservoir is heterogeneous (even with favorable mobility ratio) to recover bypassed oil.

How to design a successful pilot ?The main criteria to look at when designing a pilot injection are:

Short spacing /residence time between injection and production well to accelerate the response

Good connectivity between wells

Pattern with surrounding offset producers where incremental oil from polymer injection can be isolated for calculation

Good water injectivity good polymer injectivity

Tests to check maximum rates and viscosity accepted by reservoir

Micro-fractures can be used to improve the overall efficiency

Relatively high oil saturation( residual oil saturation)

Pilot injection can start very quickly using standard equipment.

PAM Flooding

Water Flooding

Polymer selection

Laboratory studies

Equipement Engineering Design

Field installation Commissioning start-up

Operation Maintenance

2 weeks 1-6 months 6-8 months 8 months 5 - 25years

Injectivity TestValidation of flow parameters Key learnings

Validation of technology Evaluation of recovery factors

Large scale development

Pilot Full Field

1 to 3 months

Portable injection unit

Portableselection

6 to 18 months

Skids Turn-Key systems

Dissolution/ Injection

equipement

5 to 25 years

Turn-Key systems On-site injection

plants

Logistics Polymer supply

StorageDissolution

Principles of Polymer Injection

Chemistry

Timeframe

Installations

Critical parameter

11

Chemistry

Example of an anionic co-polymer of acrylamide and acrylic acid

Two families of polymers:- Biopolymers-HPAM: Partially Hydrolyzed Polyacrylamide (synthetic polymers)Fine-tuning chemistry can help to limit shear and salt sensitivities of synthetic polymers.

SNF develops and manufactures tailor-made polymers based on acrylamide. High molecular weight hydrosoluble polymers are mainly used to increase viscosity.

Polymer / Solvent InteractionImportant notions to understand properties of polymers into solution.A polymer is able to increase the viscosity of the medium only if the chains are uncoiled: this is a medium where the polymer « feels comfortable. » What does it mean ? It means the interactions polymer / solvent should be better on the energetical point of view than the interactions polymer / polymer.

Excellent injectivity and propagation

High viscosifying power

Good and long stability in mild reservoirs condi-tions

Cost-effective, high production capacity worldwide

Non toxic

Shear sensitive

Salt and temperature sensitive

Sensitive to chemical degradation

Low biodegradability

Advantages Disadvantages

HPAM characteristics

HPAM characteristics

O O

NH+ m

Acrylamide Acrylic acidAnionic polyacrylamide

Caustic sodaC

H

H

C

H

OHO2 2

C

H

H

C

H

O

-( )nNH OCH

SNF chemistry

n,m

12

Polymer chemistry needs to be carefully selected Importance of brine characteristics. Polymer/solvent interactions describe the conformation of the polymer chains (coil) in solution Efficiency.

Polymer solvent interaction

If the interactions are good , the macromolecular chain deploys into the medium.Polymer chain expanded high viscosity

1% Polyacrylamide in H2O

(viscosity brookfield) η = 5.000 to 6.000 mPa.s (Brookfield UL @6 rpm )

1% Polyacrylamide in H2O+Ethanol (70/30)

η = 700 to 800 mPa.s __ (Brookfield UL @6 rpm )

1% Polyacrylamide in Ethanol

η = η of ethanol __ (Brookfield UL @6 rpm )

Good solvent

Viscosity depends on solvent

Collapsed polymer(MW = 8.106 Da)



H2O

70%H2O30%Ethanol

Ethanol

The medium H2O/Ethanol is a less good solvent. The polymer « feels less comfortable . »The macromolecular chain uncoils partially.

Very bad interactions.The polymer « feels very uncomfortable ».

Water is a good solvent.

Collapsed chainPolymer-Polymer interaction

Expanded chainPolymer- Solvent interaction

Low viscosity High viscosity

13

1% Polyacrylamide in H2O

η = 5.000 to 6.000 mPa.s (Brookfield UL @6 rpm )

1% Copolymer Acrylamide /AMPS in H2O

η = 20.000 to 25.000 mPa.s (Brookfield UL @6 rpm )

H2O

H2O

Expansion of the macromolecular chain by electrostatic repulsion

PolyelectrolytesPolyelectrolyte is a polymer containing electrostatic charges into the macromolecular structure.In a polar medium like H2O, the polymer is able to expand due to internal electrostatic repulsions (stretching of the chains). It results in a high viscosity.

Associatives PolymersAssociative thickenerAssociative polymers are hydrophilic polymers containing some hydrophobic groups. A network is created by hydrophobic interactions in water.These interactions create a physical network and very high viscosities can be obtained.

Hydrophobic interaction

Hydrophobic groupWater soluble polymer chain

But if salts are present/added, viscosity decreases because of a «screen effect» :- decrease of repulsions - the macromolecular chains retract- viscosity decreases

Chemistry



14

Polymer degradationand strategies to minimize it

The value of adding polymer to a waterflood can be explained by considering the mobility ratio equation with the aim to reach a value close to 1 so that oil and water have the same mobility inside the reservoir. The easiest way is to increase water viscosity as shown by the equation below.Polyacrylamides are sensitive to mechanical, thermal and chemical degradations. Guidelines exist and have to be implemented to minimize viscosity losses.There is a need to:

-Select the best chemistry and possible protective packages

-Use specific equipment to avoid shearing and oxygen ingress.

Polymer stability

Mechanical degradation is caused by singular pressure drops. Mechanical degradation through shearing devices can lead to significant reduction in viscosity.

Polyacrylamides are sensitive to shear which degrades the polymer into smaller molecules. Lower molecular weight polymers are much less sensitive to shear.

Special attention should be paid to:- Dissolution and surface injection equipment,- Velocity of the fluid,- Injection lines (restriction, chokes),- Surface of perforations,- Permeability of the reservoir,- Reduction of the injection surface by plugging

SNF has defined a set of engineering guidelines to minimize shear in the surface equipment.

M

Mobility ratio

End-point relative permeability of water

End-point relative permeability of oil

oil viscosity

water viscosity

= kw

µwko

µo

Time

Inje

ctio

n w

ell

Mechanical degradationChemical degradation

Thermal degradation Stable fluid

Hydrolysis effect

Reduced hydrodynamic volume

+ gradual effect of dilution and retention

15

Negative effect of high temperature

Temperature limits for sulfonated co-polymers AN-125ATBS based copolymer (Flopaam AN 125) w/o O2 and divalent cations

New range of polymer for high temperaturesNVP addition improves stability at high temperature w/o O2 and divalent cations

Thermal degradation is linked to polymer hydrolysis and precipitation with divalent cations.Polymer microstructure and anionicity should be carefully selected and controlled to minimize thermal degradation

Copolymers acrylamide / acrylic acid are stable up to 75°C. Above 75°C and up to 120°C, polymers containing acrylamide / ATBS or/and other thermal resistant monomers can be used (Flopaam AN 100 & Superpusher SAV series).Above 50°C, hydrolysis of the polymer will occur resulting in increased anionicity. When anionicity increases above a critical level (35% to 40%) precipitation with divalent ions (Ca2+, Mg2+) will occur resulting in viscosity loss.With medium to high temperature reservoirs, low anionicity polymers should be privileged. The quality of the manufacturing process of the polymer is essential to avoid high polydispersity.

Chemical degradation is caused by free radicals.It is essential to minimize chemical degradation by eliminating free radicals, removing oxygen and blanketing dissolution equipment

Free radicals scavengerSNF sells all its product with a minimal amount of free radical scavenger. For increased protection, specific packages (F3P) are developed by SNF and fine-tuned to every case.

Oxygen removalOxygen scavengers (ammonium bisulfite for example) decrease O2 content below 20 ppb.The amount of scavenger should be limited to avoid further degradation in case of oxygen ingress.

Nitrogen blanketingDissolution equipment can introduce a large amount of oxygen into the injected solution. It is necessary to blanket the installation under Nitrogen in order to prevent oxygen ingress.

Mg2+

Ca2+

Temperature hydrolysis :negative charge increase

Precipitation with divalents

Polymer concentration : 3 000 ppmO2 : 0ppb

Brookfield, UL Spindle, 6rpm, 85 CBrine : 50 000 TDS, no Ca2+, no carbonate

12

0

10

8

6

4

2

0 6010 20 30 40 50

Visc

osity

(cps

)

Time (days)

90˚C

100˚C

110˚C

120˚C

12

0

10

8

6

4

2

0 6010 20 30 40 50

Visc

osity

(cps

)

Time (days)

90˚C100˚C110˚C

120˚C

Chemistry

Fe2+R+

O2

R+

O2

R+

H2SO2

16

oilco

ntact

angle

water

solid

Use of surfactants and alkaline in EOR

Wettability connotes the preference of a given liquid to spread over a solid surface in the presence of a second liquid. It is quantified by the contact angle which represents a drop of liquid deposited on a flat surface: the smaller the angle, the higher the wettability. For example, one can distinguish water-wet reservoirs (with water wetting the grains) and oil-wet reservoirs (oil wetting the grains).

Factors affecting reservoir wettability- Oil composition- Rock mineralogy- Connate water composition and pH- Reservoir pressure and temperature

Interfacial Tension (IFT) It defines the tension (forces) existing between two immiscible fluids (oil and water).

Oil is left behind a waterflood because it can be:- Trapped by capillary forces- Bypassed (because of a bad mobility ratio)

EOR: How to mobilise the oil ?If bypassed: modification of the mobility ratio by increasing the viscosity of water : polymer injection

If trapped by capillary force : increase capillary number (viscous forces/capillary forces(IFT)) lower IFT by surfactant injection for instance

Surfactants are compounds that stabilize mixtures of oil and water by reducing the surface tension at the interface between the oil and water molecules. Surfactants are amphiphilic in nature i.e. they contain 2 distinct structural units:

water-wet reservoir

Exemple of water-wet medium (ϕ<90°)

oil-wet reservoir

grain

oil

water

17

Tail or hydrophobic group which has little affinity for water – this group is usually a hydrocarbon (alkyl) chain.

Head or hydrophilic group which has strong affinity for water, it can be neutral or charged.

AlkaliAlkaline waterflooding: process where the pH of injection water is increased by addition of alkali (sodium carbonate, sodium silicate, sodium hydroxide, potassium hydroxide). Alkali reacts with acidic compounds of the crude oil leading to lower IFT, emulsification of oil in water and solubilization of rigid interfacial films. Alkali may react with the rock leading to wettability alteration

In a nutshell: PolymerIncrease water viscosity

SurfactantsLower IFTChange wettability of the rockGenerate foams or emulsions

AlkalisReact with crude oil to generate soaps (surfactants)Increase pHAlter rock wettabilityAlter rock chemistry reducing adsorption of surfactants

EOR: Other processesMiscible gas injectionIn-situ combustionSteam injectionMicrobial degradation

Final goal: recover as much oil as technically and physically possible. Necessity to have a good understanding of the geology, the reservoir, the fluids…

Surfactant flush

mobilization

Solubilization (microemulsions)

Trapped Oil at Residual Saturation

Chemistry

18

SNF provides dedicated solutions and en-gineering services to design, build and operate polymer injection systems.

Frac trailer

Polymer injectivity trailer

Standard PIU 100 and PIUC 100 and PIU 300 MS

Skid based polymer system

Emulsion inversion, dilution and injection skid

Skid based ASP system

On plot polymer / ASP facilities

Offshore skids

Offshore modular construction

…

Every system is designed per customer require-ments. Standard injection units also exist for fast implementation.

1200.0

1000.0

800.0

600.0

400.0

200.0

0.0

0 0h05 0h10 0h15 0h20 0h25 0h30 0h35 0h40 0h45 0h50 0h55 1h00

FLOQUIP PSU™

Standard Mixing

FLOPAAM FP 3630 S - 10,000 ppm - 20˚C

Visc

osity

(cps

)

Dissolution Time (hours)

Expertise : Powder HydrationFLOQUIP PSU™ is a slicing unit that helps de-crease the dissolution time of powdered polymer.

Patented technology from SNF

Concentration up to 15 000 ppm

No fish eyes and no need for filtration

Nitrogen blanketing

Subsequent equipment reduced by 3x to 4x

+++++

Multi-Purpose Engineering Services

SNF in Enhanced Oil Recovery

19


FLOQUIP™ PSU – Process Connections

FLOQUIP™ PSU – Typical Flowsheet

Unloading system for big bagsPowder storage silo Mixing unit PSU 100

Agitated Maturation Tank Mother solution booster pump

High pressure injection pump Full E& I Package

Electrical control Panel & HMI System

Fire and gas detection system

Main Scope Detailed Design

Procurement & Equipment supply

FAT of the main equipmentsSkids Construction

Commissioning, SAT and Start-upVendor Data book

E&I package (VSD + MCC)E& I Cabling

Skid mounted system

OptionalWater run test

Polymer run testTraining

Operation & Supervision

PIU 100 Standard Polymer Injection Unit

Blanketing Gas (optional)

DryPolymer

Vent

MATURATION TANK

APPLICATION PUMP

FLOQUIP PSU

HOPPER

Water

Injection

1

7

3

5

4

6

2

1 Magnetic grid

2 Dosing screw feeder / Gear Motor

3 Flexible connection (weighing)

4 Feeder isolation valve

5 Wetting funnel

6 Cutting head (rotor / stator)

7 Electrical Motor / Pulleys / Belt

Polymer Powder

Nitrogen(Optional)

Primary Water

Polymer Mother Solution

Secondary Water

20

Projects

Large turn key projects

Offshore projects

Numerous skid-based project

21

Turn-key project - Dissolution

PSU 600 - Brazil PSU 1500 - USA


22

Notes

SNF SASZAC de Milieux

42163 Andrezieux CedexFRANCE

tel : + 33(0)4 77 36 86 00fax : + 33(0)4 77 36 86 96

mail : [email protected]

www.snf-group.com/

Handbook. Edition 2015

While SNF makes reasonable efforts to ensure the information is accurate and up-to-date, SNF makes no warranties or repre-sentations, express or implied, as to the accuracy, completeness, or any other aspect of the information on this document and assumes no liability in connection with any use of this information. Nothing herein shall be construed as a recommen-dation or license to use any information found that conflicts with any patent, trademark or copyright of SNF or others, and SNF makes no representations or warranties, express or implied that any use of this information will not infringe any such patent, trademark or copyright.

petroleum geology petroleum systems eor 101

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